How to Reduce Injection Mold Costs Without Compromising Quality?

Worried that cutting mold costs means sacrificing part quality? High tooling expenses can strain project budgets, forcing tough choices. But cost reduction doesn’t have to equal lower standards.

Reduce injection mold costs¹ effectively by optimizing part design² (minimize features, avoid undercuts, use core-outs), selecting appropriate mold materials for the required lifespan, increasing cavitation where feasible, and involving your mold maker early for DFM.

Finding that balance between cost and quality is a constant challenge, isn’t it? I’ve worked with many designers like Jacky who face this pressure daily. The good news is, with smart design choices and collaboration, you can significantly lower tooling investment without ending up with a subpar product or mold. Let’s explore some practical strategies you can implement right from the design phase. These steps can make a real difference to your bottom line.

Can Minimizing Unnecessary Features Really Lower Mold Cost?

Think simplifying your part design might save mold costs? Overly complex parts with non-essential features directly increase tooling expenses and manufacturing time. Focus on what truly adds value.
Yes, minimizing features like tight tolerances where unnecessary, complex textures, decorative ribs, or seldom-seen logos significantly cuts machining time, reduces mold complexity, potentially avoids costly EDM, and lowers overall mold cost.

Diving Deeper: The Impact of Feature Complexity

Every feature added to a part design translates into work on the mold steel. The more intricate the design, the more time and specialized processes are needed to create the mold, directly impacting the final cost.

• Tolerances: Holding extremely tight tolerances (+/- 0.001 inches or less) requires precision machining, multiple finishing steps, and potentially slower CNC feed rates. It also demands more rigorous quality control during mold making. Ask yourself: Does every feature need this level of precision? Relaxing tolerances on non-critical dimensions saves significant machining and inspection time. I recall a project where loosening tolerances on internal, non-mating features saved nearly 10% on the mold cost alone.
• Surface Finishes & Textures: High-gloss polished finishes (SPI A-1, A-2) require hardened stainless steel and extensive, highly skilled manual labor for polishing. Complex or very fine textures often necessitate EDM (Electrical Discharge Machining¹), which is slower and more expensive than standard CNC milling. Opting for a standard SPI finish (like B-2 or C-1) or a simpler texture where aesthetics allow can offer substantial savings.
• Non-Functional Elements: Features like embossed logos in hidden areas, purely decorative ribs, or unnecessary chamfers/radii add complexity to the mold cavity or core. Each one needs to be accurately machined. Eliminating or simplifying these non-essential elements streamlines the mold build.
• Number of Features: Simply put, more features mean more programming time for CAM (Computer-Aided Manufacturing²), more machine setup time, and more cutting tool paths. Each transition, corner, and surface adds to the overall machining hours.
  Engaging in thorough Design for Manufacturability (DFM) analysis early, often with your mold maker like us at CavityMold, is crucial. We can help identify features that add disproportionate cost relative to their functional or aesthetic value. Streamlining the design is often the most effective first step in controlling mold costs.

Does Choosing Less Expensive Mold Steel Always Make Sense?

Tempted to specify cheaper mold steel to cut upfront costs? While material cost is a factor, choosing the wrong steel can lead to bigger expenses down the line. It’s a critical decision based on project needs.

Choosing less expensive steel (like Aluminum or pre-hardened P20) saves initial cost but is only suitable for lower production volumes. Hardened steels (H13, S7, S136) cost more upfront but are essential for high volumes, abrasive materials, or high polish, preventing premature wear and costly repairs.

Diving Deeper: Matching Steel to Project Requirements

The type of steel used for the mold’s core and cavity is a fundamental cost driver, but it’s directly linked to the mold’s expected lifespan and the type of plastic being molded. Choosing inappropriately can be a costly mistake.

• Production Volume is Key: This is often the primary deciding factor.
  • Low Volume / Prototyping (<10,000 shots): Aluminum (like 7075) is fast to machine and cheap, ideal for quick prototypes or very short runs. However, it wears quickly and is easily damaged.
  • Medium Volume (50,000 – 500,000 shots): Pre-hardened steels like P20 are a common choice. They offer a good balance of machinability, durability, and cost. They are suitable for many consumer product applications.
  • High Volume (500,000+ shots): Hardened tool steels like H13 or S7 are necessary. They require heat treatment after rough machining, adding cost and time, but offer excellent wear resistance for long production runs.
• Plastic Resin Considerations: The material being molded influences steel choice.
  • Abrasive Fillers (e.g., Glass Fiber): These fillers rapidly wear down softer steels. Hardened steels (H13, S7) are essential to resist abrasion and maintain tolerances over the mold’s life. Using P20 with highly abrasive material would lead to rapid tool wear and failure.
  • Corrosive Resins (e.g., PVC): These materials release corrosive gases during molding. Stainless mold steels like S136 are required to prevent rust and pitting, especially for parts needing a high polish.
• Surface Finish Requirements: Achieving and maintaining a high-gloss polish (SPI-A range) typically requires high-hardness stainless steels (like S136) that can take and hold the polish. P20 generally can only be polished to a B-range finish.
• The True Cost: While hardened steel increases the initial mold price (material cost + heat treatment + potentially slower final machining), it prevents the much larger costs associated with premature mold failure, frequent repairs, production downtime, and potentially needing to build a replacement mold mid-project. I’ve seen clients try to save money using P20 for high-volume projects, only to face significant repair costs and production delays later. Choosing the right steel for the job is crucial for overall project success and cost-effectiveness. It’s not just about the upfront price tag.
  

  How Much Can Eliminating or Reducing Undercuts Save?

  Are undercuts in your part design unavoidable? These features, which prevent a part from being ejected straight out of the mold, significantly increase mold complexity and cost. Addressing them is key.

Eliminating undercuts removes the need for complex side-actions (sliders, lifters) in the mold. This drastically reduces mold cost by simplifying design, machining, assembly, and maintenance, while also improving mold reliability.

Diving Deeper: The Cost of Complexity from Undercuts

Undercuts are design features like recessed clips, side holes, or inward-facing tabs that are not parallel to the direction the mold opens and closes. They create an "overhang" that traps the part. To release such features, the mold needs mechanical components that move perpendicular to the main mold action.

• Side Actions Explained:
  • Sliders (or Slides): These are blocks of steel that move laterally (sideways) to form the undercut feature and then retract before the part is ejected. They are typically driven by angled pins or hydraulic/pneumatic cylinders.
  • Lifters: These components move at an angle relative to the ejection direction, often mounted on the ejector plate. As the ejector system moves forward, the lifter moves both up and sideways to clear the undercut before fully ejecting the part.
• Why They Add Cost:
  • Design Complexity: Designing sliders and lifters requires careful calculation of angles, travel distances, clearances, and integration with the mold base and ejection system. This adds significant engineering hours.
  • Machining & Fitting: These components require precise machining (often including complex angles and surfaces) and meticulous hand-fitting by skilled mold makers to ensure smooth, reliable operation without flashing (plastic leaking). This is labor-intensive.
  • Mold Base Size: Side actions often require a larger, more complex, and thus more expensive mold base to accommodate the mechanisms.
  • Maintenance & Reliability: Sliders and lifters are moving parts that experience wear and tear. They require regular maintenance (lubrication, cleaning) and are potential failure points that can halt production. Complex actions increase the risk of mold damage if something goes wrong (e.g., ejecting before a slider fully retracts).
• Design Alternatives: Before committing to an undercut, explore alternatives with your team and mold maker:
  • Relocating the Feature: Can the clip or hole be moved to avoid the undercut?
  • Using Snap Fits: Design mating parts with snap-fit features created in the line of draw.
  • "Sliding Shutoffs" or Pass-Through Cores: Clever design can sometimes create holes or features using sections of the core and cavity that meet and seal ("shut off") when the mold closes, avoiding the need for action.
  • Redesigning the Feature: Can the function be achieved differently without the undercut geometry?
    While sometimes unavoidable, actively designing out undercuts is one of the most impactful ways Jacky and other designers can reduce mold cost, complexity, and potential production headaches. Each eliminated side action can save thousands of dollars.

    Why Use Core Cavity Approaches for Thin-Walled Designs?

    Striving for thin walls in your part design? Simply making walls thin isn’t enough; how you achieve thinness impacts mold cost, part quality, and production efficiency. Coring out is often the answer.

Using a core-cavity approach (coring out) to create thin walls ensures uniform wall thickness. This improves plastic flow, reduces sink marks, shortens cycle times, uses less material per part, and simplifies mold cooling, often lowering overall project costs despite a potentially more complex mold shape.

Diving Deeper: The Benefits of Coring for Thin Walls

Creating thin-walled parts isn’t just about saving plastic; it’s about designing for efficient and high-quality molding. Trying to mold parts with thick sections alongside thin sections causes problems. Coring out non-functional thick sections to achieve uniform thinness is best practice.

• Uniform Wall Thickness: This is the primary goal. Plastic flows best when it doesn’t have to transition between thick and thin sections abruptly. Uniform walls ensure consistent filling pressure, reduce the chance of voids or weak points, and minimize differential shrinkage which causes warping.
• Reduced Material Consumption: Coring out thick sections directly reduces the volume of plastic needed per part. Over a long production run, this material saving can be substantial, significantly lowering the cost per part. Even a small reduction in shot weight adds up quickly over hundreds of thousands of cycles.
• Faster Cycle Times: Thicker sections take much longer to cool than thin sections. By maintaining uniform thin walls, the entire part cools faster and more evenly. This allows for significantly shorter cycle times, increasing production throughput and lowering the molding cost per part (less machine time needed). I’ve seen cycle times cut by 20-30% just through proper coring.
• Improved Part Quality: Uniform cooling prevents sink marks (depressions on the surface opposite thick sections like ribs or bosses) and reduces internal stresses that can lead to warping or premature failure. The part is stronger and more dimensionally stable.
• Mold Design Considerations: While creating the core geometry to hollow out the part adds complexity to the mold’s machining compared to a simple blocky shape, the benefits usually outweigh this. It allows for more straightforward cooling channel design within the core and cavity, focused on efficiently cooling the uniform wall. Trying to cool a part with vastly different thicknesses is much harder and less effective.
• Core-Cavity vs. Simple Cavity: Instead of just sinking the part shape into one side of the mold (simple cavity), the core-cavity approach uses a mating core pin or block on one side and the cavity on the other to define both the inner and outer surfaces of the thin-walled feature. This detailed shaping capability is essential for controlled, uniform walls.
  For designers like Jacky focused on optimizing parts for production, thinking about "coring out" rather than just "making it thin" is crucial. It impacts mold design, material usage, cycle time, and final part quality – all contributing to overall project cost-effectiveness.

  Conclusion

  Reducing injection mold costs without losing quality is achievable through smart design choices and collaboration. Focus on feature necessity, appropriate materials, avoiding undercuts, and optimizing wall thickness via coring for best results.